An ordinary wire heats up when current flows through it — some energy is wasted. A superconductor lacks this flaw: electricity flows through it without loss, like water through a perfectly smooth pipe. The trouble is that most superconductors require either very low temperatures or colossal pressures, like those found in the depths of planets.
Chemists have long sought materials that would suffice with moderate conditions. Hydrides, compounds of metals with hydrogen, were considered promising, but record holders required pressures in the hundreds of gigapascals. That's like holding a sample under the weight of tens of thousands of elephants on a square centimeter. The new material Mg2RhH6 changes the game: it becomes superconducting at just 30 GPa — three times lower than previous values.
The synthesis proceeded in two steps. First, a precursor Mg2RhH5 was obtained, where hydrogen atoms are held by strong bonds. Then more hydrogen was added, and above 30 GPa the structure rearranged: pyramids of rhodium and hydrogen atoms turned into octahedra. It is this new geometry that allowed electrons to fill special states and trigger superconductivity.
At 30 GPa, the material stopped resisting current at 24 K — about minus 249 degrees Celsius. Cold, but not cosmic frost. At 53 GPa, the temperature rose to 29 K. Most importantly, the compound is thermodynamically stable, meaning it does not spontaneously decompose. So it can be studied and possibly used.
The path to superconductors operating at room temperature and ordinary pressure is long. But every step toward lower pressure is a step toward lossless wires, powerful magnets, and new technologies. Mg2RhH6 shows that you don't have to compress matter to planetary pressures to make it conduct electricity perfectly.
At 30 GPa, the distance between atoms shrinks by about 10–15%—as if a person's height decreased by a head.
In Arthur C. Clarke's novel 'Childhood's End', aliens use superconductors for levitation, but they don't specify at what pressure they work.